To continue charging while a failure such as deterioration and expansion of a battery is reduced even if a battery temperature rises.

A protection operation control part (protection operation control IC) 245 detects an overcharge state, and on/off-controls an overcharge protection transistor. A reference temperature judging unit 252 in a battery pack 240 detects that the battery temperature becomes not less than a reference temperature. A charging/discharging judging unit 253 judges whether or not the present state is charging or discharging. When the battery temperature becomes not less than the reference temperature at the time of charging, the overcharge protection transistor 255 is controlled so that an ON resistance value becomes an intermediate value between zero and infinite.

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